The present invention relates to a structure for transport and offshore installation of at least one wind turbine or underwater generator.
The invention also relates to methods for transport and offshore installation of at least one wind turbine or underwater generator using such a structure.
Traditionally, wind turbines or underwater generators include a mast having a nacelle containing an electrical production means driven by blades.
The mast is mounted on a base secured on the ground or on a sea bottom for an offshore installation.
In the case of wind turbines, the nacelle is fastened to the upper end of the mast and the blades are driven in rotation by the wind.
In the case of underwater generators, the nacelle supported by the mast is placed below the surface of the water and the blades are driven in rotation by the ebb and flow of the water.
The offshore installation of wind turbines or underwater generators consists of placing and fixing the base on the sea bottom, then bringing, most often by transport vessel, the other part of the wind turbines or underwater generators, i.e. the mast bearing the nacelle and the blades.
The mast bearing the nacelle and the blades is placed on the base using different methods.
One known method consists of transporting the mast in a vertical position and suspending said mast from a hoisting apparatus, e.g. a crane supported by a vessel, then gradually lowering the mast using the crane to engage its lower end in the base.
Another known method consists of transporting the mast equipped with its nacelle and its blades in the horizontal position on a vessel, then tilting the mast into a vertical position and gradually lowering the mast using a guide column in order to engage its lower end in the base.
But these known methods have a significant drawback.
Indeed, during the gradual lowering of the mast, the mast is borne by a vessel that is subject to the motion of the swell, with the result that the mast oscillates, which requires that its lower end be held to engage it in the base.
Once its lower end is engaged in the base, the mast still undergoes the motions of the vessel, which can cause significant stresses or strains in the base and buckling of the mast as long as the mast is connected to the vessel.